The present invention relates generally to new and novel improvements in stencils having enhanced wear-resistance, and to methods of manufacturing the same. More particularly, the present invention relates to stencils which may be used, in one advantageous application, for printing solder paste onto the contact pads of printed circuit boards. Stencils in accordance with the present invention are also useful in other applications, including printing processes where the stencils are subjected to mechanical pressure.
Printed circuit boards designed to receive surface-mounted components are often provided with a plurality of contact pads on their surface. Surface-mounted components are mounted by way of connector leads on the individual surface-mounted component's body. In order to mechanically and electrically connect the connector leads of the components to the contact pads of the printed wiring board, the contact pads are typically provided with a layer of solder paste prior to placement of the connector leads thereon. Once the surface-mounted component has been positioned on the appropriate contact pads, the solder paste is melted and subsequently solidifies to form a mechanical and electrical connection between the connector leads of the surface-mounted component and the contact pads.
Metal stencils are often employed to apply the solder paste onto the contact pads. Such stencils typically have a plurality of apertures which are positioned in the stencil in a predetermined pattern to correspond with the pattern of contact pads on a particular printed circuit board.
In use, such stencils are positioned on the surface of the printed circuit boards having the contact pads upon which solder paste is to be applied. The apertures in the stencil are then aligned over the contact pads onto which solder paste is to be applied. Solder paste is then urged mechanically by, for example, a squeegee, across the upper surface of the stencil and through the apertures in the stencil. Islands of solder paste is thereby accurately located on the appropriate contact pads.
These types of stencils are commonly employed in high-volume production processes. However, one disadvantage of many known stencils is that the stencil quality deteriorates quickly due to damage caused by the mechanical pressure which is applied by the squeegee as it passes over the stencil surface and solder paste is urged into the apertures, and subsequently onto the contact pads. In particular, the edges at the junction between the upper surface of the stencil and the side walls of the apertures become rounded and generally damaged, thus leading to a reduction in the quality and definition of the resulting solder paste pattern. Thus, the useful service life of such known stencils is disadvantageously restricted.
Accordingly, an object of the present invention is to provide stencils having enhanced wear-resistance which are resistant to damage and capable of extended service life, and manufacturing methods for making the same.
Another object of the present invention is the provision of stencils having enhanced wear-resistance which can be used for applying solder paste onto contact pads of printed circuit boards and which are resistant to damage and capable of extended service life, and manufacturing methods for making the same.
These and other objects of the present invention are attained by the provision of a stencil having a metal body having first and second major surfaces, and at least one aperture passing through the body from the first major surface to the second major surface. In one preferred embodiment of the present invention, the side wall surfaces of the apertures and at least one of the first major surface and second major surface has a thin diamond coating thereon. Preferably, the diamond coating is applied as a thin film by a low pressure synthesis process.
It should be understood that the term diamond as used in the present description and claims refers to a transparent and hard synthetic carbon material having properties which resemble natural diamonds. Such materials are commonly known in the art as synthetic diamonds or diamondlike carbon.
Other objects, advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.